[RFC PATCH v2 12/22] sound: usb: card: Introduce USB SND platform op callbacks

[Wesley Cheng]

Hi Pierre,

On 1/26/2023 7:50 AM, Pierre-Louis Bossart wrote:
> 
> 
> 
>> +int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops)
>> +{
>> +	if (platform_ops)
>> +		return -EEXIST;
>> +
>> +	platform_ops = ops;
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(snd_usb_register_platform_ops);
>> +
>> +int snd_usb_unregister_platform_ops(void)
>> +{
>> +	platform_ops = NULL;
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(snd_usb_unregister_platform_ops);
> 
> I find this super-racy.
> 
> If the this function is called just before ...
> 
>>   
>>   /*
>>    * disconnect streams
>> @@ -910,6 +928,10 @@ static int usb_audio_probe(struct usb_interface *intf,
>>   	usb_set_intfdata(intf, chip);
>>   	atomic_dec(&chip->active);
>>   	mutex_unlock(&register_mutex);
>> +
>> +	if (platform_ops->connect_cb)
>> +		platform_ops->connect_cb(intf, chip);
>> +
> 
> ... this, then you have a risk of using a dandling pointer.
> 
> You also didn't test that the platform_ops != NULL, so there's a risk of
> dereferencing a NULL pointer.
> 
> Not so good, eh?
> 
> It's a classic (I've had the same sort of issues with SoundWire), when
> you export ops from one driver than can be removed, then additional
> protection is needed when using those callbacks.
> 
> 

Yep, will take a look at this a bit more to improve it.

Thanks
Wesley Cheng